Time Domain and Fourier Domain

OCT• Quick Configurations

• Time Domain OCT• Time Domain Signal for δ-like Object

• Missing facts

• More realistic example

• Possible solution

• Fourier Domain OCT• Fourier Domain OCT• Fourier Domain Signal for δ-like Object

• Noise removal

• More realistic example

• Diffraction Effects in FD-OCT• Born Approximation

• Direct application to the OCT

• Rytov Approximation

• Direct application to the OCT

Time Domain OCT

Fourier Domain OCT

Time Domain Signal

What is missing in conventional

TD-OCT

� Refractive index of the whole sample has been

considered constant.

� Reflectivity of each layer does not depend on

the refractive index. the refractive index.

Layered sample with different

refractive indices

z0

z1

z2

z3

n0

n1

n2

n3z3 n3

Main difficulty arises here is that the thickness and

refractive index are coupled together

Possible solution: oblique illumination

Successive Interferograms

Maximizing the first term yields:

Maximizing the second layer in two different angles yield:

Just functions of n1 constants

The left hand side is just the function of n1 and

may be solved for the refractive index.

FD-OCT

More deeper into the sample corresponds to higher frequency detection

Noise removalFT removes DC and Autocorrelation terms FT removes mirror image

Layered sample with different

refractive indices

z0

z1

z2

z3

n0

n1

n2

n3z3 n3

Main difficulty arises here is that the thickness and

refractive index are coupled together

Diffraction Effects in FD-OCT

Helmholtz eq.

Scattering Potential

Born Approximation

Using the angular spectrum representation yields

Born approximation works well

just for very small objects

Direct application to the OCT

Rytov Approximation

Rytov ApproximationRytov Approximation

Direct application to the OCT

the power spectrum of the

light source does not play a

role.